1. Field of the Invention
Enhancements to a video anticopy process, the enhancements causing additional degradation to the picture quality when a copy of a protected recording is played back, and additionally which reduce the viewability of unauthorized recordings of the protected recording.
2. Description of the Prior Art
Video anticopy processes are well known. An example is Ryan, U.S. Pat. No. 4,631,603 issued Dec. 23, 1986, incorporated by reference which discloses (see Abstract):
"A video signal is modified so that a television receiver will still provide a normal color picture from the modified video signal while the video tape recording of the modified video signal produces generally unacceptable pictures. This invention relies on the fact that typical videocassette recorder automatic gain control systems cannot distinguish between the normal sync pulses (including equalizing or broad pulses) of a conventional video signal and added pseudo-sync pulses. Pseudo-sync pulses are defined here as any other pulses which extend down to normal sync tip level and which have a duration of at least 0.5 microseconds. A plurality of such pseudo-sync pulses is added to the conventional video signal during the vertical blanking interval, and each of said pseudo-sync pulses is followed by a positive pulse of suitable amplitude and duration. As a result, the automatic gain control system in a videotape recorder will make a false measurement of video level which causes an improper recording of the video signal. The result is unacceptable picture quality during playback."
Column 2, beginning at line 5 states that the added pulse pairs (each pair being a negative-going pseudo-sync pulse followed by a positive-going "AGC" pulse) cause an automatic level (gain) control circuit in a videotape recorder to erroneously sense video signal level and produce a gain correction that results in an unacceptable videotape recording.
Therefore this prior art "basic anticopy process" causes an abnormally low amplitude video signal to be recorded when a copy is attempted. Some of the effects observed when the illegal copy is replayed are horizontal tearing (positional displacement) and vertical displacement of the picture. Whether this occurs or not is often largely dependent on the picture content, i.e. presence of white (light) and black (dark) areas in the picture. Therefore this prior art process, while generally providing excellent copy protection, with some combinations of videotape recorders (such as VCRs) and television sets provides a picture viewable by persons willing to tolerate a poor quality picture.
Also, with certain VCRs and TV sets the various well known prior art copy protection processes provide little picture degradation. Certain markets for prerecorded video material have a high rate of piracy, i.e. illegal copying of videotapes, in spite of copy protection and these viewers apparently are relatively insensitive to the poor quality picture in illegal copies caused by the prior art copy protection processes. Thus there is a need for copy protection process enhancements which degrade the quality of the picture even more than that of the prior art processes.